Thermal Properties Of Skin Research Articles

Dietary lipid is largely deposited in skin and rapidly affects insulating properties.

Skin has been shown to be a regulatory hub for energy expenditure and metabolism: mutations of skin lipid metabolism enzymes can change the rate of thermogenesis and susceptibility to diet-induced obesity. However, little is known about the physiological basis for this function. Here we show that the thermal properties of skin are highly reactive to diet: within three days, a high fat diet reduces heat transfer through skin. In contrast, a dietary manipulation that prevents obesity accelerates energy loss through skins. We found that skin was the largest target in a mouse body for dietary fat delivery, and that dietary triglyceride was assimilated both by epidermis and by dermal white adipose tissue. Skin from mice calorie-restricted for 3 weeks did not take up circulating lipids and showed a highly depleted stratum corneum. Dietary triglyceride acyl groups persist in skin for weeks after feeding. Using multi-modal lipid profiling, we have implicated both keratinocytes and sebocytes in the altered lipids which correlate with thermal function. In response to high fat feeding, wax diesters and ceramides accumulate, and triglycerides become more saturated. In contrast, in response to the dramatic loss of adipose tissue that accompanies restriction of the branched chain amino acid isoleucine, skin becomes more heat-permeable, resisting changes induced by Western diet feeding, with a signature of depleted signaling lipids. We propose that skin should be routinely included in physiological studies of lipid metabolism, given the size of the skin lipid reservoir and its adaptable functionality.

Monitoring of some minor human skin lesions using a skin calorimeter

The growing interest of human skin thermal properties is motivating the development of new instruments, either by contact or by remote sensing. In this work, we show the ability of a skin calorimeter to monitor the temporal evolution of the heat capacity and the equivalent thermal resistance of the skin, in two small skin lesions. The first one consists of a forehead wound of 10 × 2 mm2. The other injury consists of a second degree burn on the volar wrist area, of 10 × 20 mm2. We studied the temporal evolution of the thermal properties of both injuries. The variation of heat capacity was significant. For first injury, heat capacity decreased by 21% and full recovery was achieved after ten days. For the second case, the heat capacity decrease was 55% and recovery was achieved after 3 weeks. These skin recoveries are monitored by the measured heat capacity value. The returning of the heat capacity to its normal value coincides with the recovery from the injury.

Variations of skin thermal diffusivity on different skin regions.

Skin thermal diffusivity plays a crucial role in various applications, including laser therapy and cryogenic skin cooling.This study investigates the correlation between skin thermal diffusivity and two important skin parameters, melanin content and erythema, in a cohort of 102 participants. An in-house developed device based on transient temperature measurement was used to assess thermal diffusivity at different body locations. Melanin content and erythema were measured using a colorimeter. Statistical analysis was performed to examine potential correlations. The results showed that the measured thermal diffusivity values were consistent with previous reports, with variations observed among subjects. No significant correlation was found between thermal diffusivity and melanin content or erythema. This suggests that other factors, such as skin hydration or epidermis thickness, may have a more dominant influence on skin thermal properties. This research provides valuable insights into the complex interplay between skin thermal properties and physiological parameters, with potential implications for cosmetic and clinical dermatology applications.

Advanced approaches for quantitative characterization of thermal transport properties in soft materials using thin, conformable resistive sensors

Noninvasive methods for precise characterization of the thermal properties of soft biological tissues such as the skin can yield vital details about physiological health status including at critical intervals during recovery following skin injury. Here, we introduce quantitative measurement and characterization methods that allow rapid, accurate determination of the thermal conductivity of soft materials using thin, skin-like resistive sensor platforms. Systematic evaluations of skin at eight different locations and of six different synthetic skin-mimicking materials across sensor sizes, measurement times, and surface geometries (planar, highly curvilinear) validate simple scaling laws for data interpretation and parameter extraction. As an example of the possibilities, changes in the thermal properties of skin (volar forearm) can be monitored during recovery from exposure to ultraviolet radiation (sunburn) and to stressors associated with localized heating and cooling. More generally, the results described here facilitate rapid, non-invasive thermal measurements on broad classes of biological and non-biological soft materials.

Simplified human thermoregulatory model for designing wearable thermoelectric devices

Research on wearable and implantable devices have become popular with the strong need in market. A precise understanding of the thermal properties of human skin, which are not constant values but vary depending on ambient condition, is required for the development of such devices. In this paper, we present simplified human thermoregulatory model for accurately estimating the thermal properties of the skin without applying rigorous calculations. The proposed model considers a variable blood flow rate through the skin, evaporation functions, and a variable convection heat transfer from the skin surface. In addition, wearable thermoelectric generation (TEG) and refrigeration devices were simulated. We found that deviations of 10–60% can be resulted in estimating TEG performance without considering human thermoregulatory model owing to the fact that thermal resistance of human skin is adapted to ambient condition. Simplicity of the modeling procedure presented in this work could be beneficial for optimizing and predicting the performance of any applications that are directly coupled with skin thermal properties.

A Simplified Thermal Model and Comparison Analysis for a Stratospheric Lighter-Than-Air Vehicle

Transient thermal behavior modeling and simulation is a key issue in predicting flight performance of stratospheric lighter-than-air (LTA) vehicles, such as airships or balloons. To reduce computational load of the transient thermal model without significant loss of accuracy, first this paper adopted an analytical model of view factor from the element surfaces to the Earth and constructed a full distributed parameter transient thermal model. Then, the full model was validated by comparing the predictions obtained from the full model with the flight experimental data. The comparison results show that the divergence of the predicted average internal gas temperatures from the flight data is about 0.4%, and the divergence of the predicted envelop temperatures from the flight data is less than 2.4%. Furthermore, considering that the effect of the net radiation heat transfer among the inner surface enclosure on average internal gas temperature is far less than radiation heat transfer of the outer surfaces, the full model was simplified by omitting radiant heat exchange within the inner surface enclosure. The accuracy of the simplified model was investigated by comparing the predictions of average internal gas temperature and skin temperature distribution between the simplified model and full model under various conditions, such as flight time, altitude, and different external skin thermal properties. The comparison results indicate that the simplified model agrees well with the full model. The discrepancies of the predicted average internal gas temperature between the two models are less than 0.3% under most conditions, and the discrepancies of the predicted temperature distribution between the two models are also acceptable when the LTA vehicle, especially with low absorptivity/emissivity ratio coatings, operates at about 20 km altitude.

Measurement of the Heat Removed by Devices for Skin Tags Treatment

This paper describes a method for the comparison of the cooling capability of over-the-counter devices for skin tags removal. The comparison is performed by measuring the heat flux produced by the gas identified assessing the temperature difference across an element with a known thermal resistance; the temperature reached at the interface between the device and the heat-flux meter is also analyzed, although it is different from that of the skin during the treatment. The measurement accuracy has been experimentally evaluated and, with a confidence interval of 95%, is better than 6% for heat-flux measurements and lower than 0.3 °C for temperature measurements. The instrument allowed comparing the thermal efficiency of 19 dimethyl ether and propane devices of different types (dispenser, spray, and foam). Results are by far more reliable than those obtained with tests performed on subjects, where the intrinsic skin thermal properties variability prevents from assessing differences smaller than 30%.

A Device for the Skin–Contact Thermal Resistance Measurement

The skin-contact thermal resistance is a parameter that allows evaluating, in steady condition, the heat flow at the interface between the skin and a rigid surface at a known temperature. At the current state of the art, it is evaluated with empirical equations and is known to be dependent on the contact pressure, on the surface characteristics, and on the skin conductivity. The need to measure skin and contact thermal resistance with low uncertainty led to the realization of the device described in this paper. The instrument - based on the principle of the thermoflowmeter - has been designed with the goal of minimizing the measurement uncertainty with contact temperatures ranging between 12 °C and 27 °C and contact areas from 50 to 314 mm2. The device allows varying and controlling the interface pressure and temperature that, according to existing literature studies, are likely to influence the skin thermal properties. The different temperatures needed for the evaluation of the thermal resistance are measured with individually calibrated thermocouples. The metrological characterization of the flowmeter was performed under vacuum, and the effect of convective heat exchanges in normal operation was modeled and compensated. Measurement repeatability and reproducibility were assessed by measuring the thermal resistance of plastic materials in operational conditions. Preliminary tests showed that the skin-contact thermal resistances measured in different conditions are compatible with the theoretically evaluated ones, with improvement in uncertainty due to direct measurement.

Transport lattice models of heat transport in skin with spatially heterogeneous, temperature-dependent perfusion.

BackgroundInvestigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. Transport of heat by conduction, and by temperature-dependent, spatially heterogeneous blood perfusion is modeled here using a transport lattice approach.MethodsWe represent heat transport processes by using a lattice that represents the Pennes bioheat equation in perfused tissues, and diffusion in nonperfused regions. The three layer skin model has a nonperfused viable epidermis, and deeper regions of dermis and subcutaneous tissue with perfusion that is constant or temperature-dependent. Two cases are considered: (1) surface contact heating and (2) spatially distributed heating. The model is relevant to the prediction of the transient and steady state temperature rise for different methods of power deposition within the skin. Accumulated thermal damage is estimated by using an Arrhenius type rate equation at locations where viable tissue temperature exceeds 42°C. Prediction of spatial temperature distributions is also illustrated with a two-dimensional model of skin created from a histological image.ResultsThe transport lattice approach was validated by comparison with an analytical solution for a slab with homogeneous thermal properties and spatially distributed uniform sink held at constant temperatures at the ends. For typical transcutaneous blood gas sensing conditions the estimated damage is small, even with prolonged skin contact to a 45°C surface. Spatial heterogeneity in skin thermal properties leads to a non-uniform temperature distribution during a 10 GHz electromagnetic field exposure. A realistic two-dimensional model of the skin shows that tissue heterogeneity does not lead to a significant local temperature increase when heated by a hot wire tip.ConclusionsThe heat transport system model of the skin was solved by exploiting the mathematical analogy between local thermal models and local electrical (charge transport) models, thereby allowing robust, circuit simulation software to obtain solutions to Kirchhoff's laws for the system model. Transport lattices allow systematic introduction of realistic geometry and spatially heterogeneous heat transport mechanisms. Local representations for both simple, passive functions and more complex local models can be easily and intuitively included into the system model of a tissue.

Measurement of the thermal inertia of the skin using successive thermograms taken at a stepwise change in ambient radiation temperature

Skin thermal properties are difficult to measure in vivo in the steady state because there is a constant temperature gradient across the skin surface. However, measurement of skin thermal properties is postulated in quantitative evaluation for thermographic observation. Here, imaging of the thermal inertia of the skin was attempted by thermographic measurements at a stepwise change in ambient radiation temperature achieved by quickly switching 2 hoods maintained at different temperatures. Using this technique, a total of 65 thermograms were sequentially recorded at intervals of 0.5 s beginning 2 s before the stepwise change. The image of skin thermal inertia was estimated by applying statistical curve fitting at each pixel of the thermograms. In addition, the emissivity and true temperature of the skin were also determined, together with thermal inertia, in a single measurement. Measurements were made at different sites on 10 subjects. The average values of thermal inertia of normal skin were scattered throughout a range from 1.4*103 to 2.1*103 W s1/2 m-2 K-1. Investigations of the relationship between skin blood flow and thermal inertia were also made by imaging thermal inertia when skin blood flow was changed by applying a vasodilator or vasoconstrictor on the skin surface. In a comparison with the data measured by laser Doppler flowmetry, the average slope of skin blood flow versus thermal inertia was 2.88*10-4 V per W s1/2 m-2 K-1, and the thermal inertia of the skin with no blood flow was 1.03*103 W s1/2 m-1 K-1. The results also show an almost linear correlation between skin blood flow and thermal inertia in each individual, but interindividual differences were also observed. The results suggest that skin blood flow distribution can be estimated by noncontact imaging of thermal inertia.

Improvement of imaging of skin thermal properties by successive thermographic measurements at a stepwise change in ambient radiation temperature

Imaging of skin thermal properties was attempted by successive thermographic measurements of the skin surface with a stepwise change in ambient radiation temperature. In order to produce the stepwise change in ambient radiation temperature, two hoods maintained at different temperatures, 20 degrees C and 60 degrees C, were mechanically switched. A total of 65 thermograms were taken from 2 s before to 32 s seconds after the hood switching. Images of skin emissivity, emissivity-corrected skin temperature and thermal inertia were obtained by least-squares fitting at each pixel of 64 thermograms. Measurements were performed on the forehead, cheek, forearm, palm and back of the hand of 10 healthy male subjects. Differences in emissivity between sites and subjects were insignificant. Significant differences were observed in thermal inertia values between sites. Great improvements in the imaging of thermal inertia have been achieved by applying least-squares fitting to 64 thermograms instead of by computations from only two thermograms as in the previous study. Non-contact measurement and visualization of skin thermal properties are significant advantages of this method.

Thermal properties calculated from measured water content as a function of depth in porcine skin

In order to develop a realistic tissue water boiling routine for a mathematical model of burn development, it was necessary to know the water content and the thermal properties of skin as a function of depth. Split thickness skin samples were obtained from several pigs using an air-powered dermatome. Alternate segments of these skin slices were processed for skin water content determination and for histopathologic measurements of skin thickness. Tissue samples were weighed, dried and subsequently weighed again using standardized methods to determine tissue water content. In some instances the volume of tissue was also determined to allow the calculation of tissue density. Given a table of measured values of water content as a function of skin thickness, a least-squares cubic polynomial was fitted to the data and water content as a function of depth was computed from the following formula: w( T- d) = Tld× ( W T - W T- d ) + W T- d where T is the total thickness of a skin slice, W T is the fraction of water computed from the cubic equation, d is the thickness of the skin slice at a depth T- d, and W T- d is the fraction of water above the thin slice. Stratum corneum hydration was calculated from measured ambient relative humidity based on a relationship previously described by Rushmer et al. (1966). Skin thermal properties as a function of depth were calculated using the formulation of Cooper and Trezek (1971). Computer simulations incorporating these new thermal properties and the water profile into our previously presented model (Knox et al., 1978 a) show that these changes have resulted in improved predicted burn depths as judged by reduced root mean square (r.m.s.) error. Using this method studies can now be made of the changes in thermal properties which occur during various stages of thermal tissue damage, e.g. oedema, protein coagulation and shrinkage due to desiccation.